1. Field of the Invention
The present invention relates generally to a waveform analyzer such as a spectrum analyzer and a network analyzer, and more particularly to a spectrum analyzer wherein an input signal is continuously frequency-converted to detect a spectrum of the input signal, and the spectrum is displayed with the magnitude thereof plotted on the ordinate and with the frequency thereof plotted on the abscissa and to a network analyzer wherein an input signal is continuously supplied to a device under tested with a variable frequency to detect an output signal of the device under tested, and the output signal is displayed with the magnitude thereof plotted o the ordinate and with the frequency thereof plotted on the abscissa.
This invention also relates to a spectrum analyzer wherein a spectrum measured in a certain band width is displayed on a first display unit as a wide-band spectrum, a desired part of the wide-band spectrum is designated by a zone marker, and the designated part is enlarged and displayed on a second display unit as a narrow-band spectrum. When the wide-band spectrum displayed on the first display unit and the narrow-band spectrum displayed on the second display unit are observed and the measurement conditions are determined, easy observation and operation is ensured.
This invention also relates to a network analyzer wherein a transmission characteristic measured in a certain band width is displayed on a first display unit as a wide-band transmission characteristic, a desired part of the wide-band transmission characteristic is designated by a zone marker, and the designated part is enlarged and displayed on a second display unit as a narrow-band transmission characteristic. When the wide-band transmission characteristic displayed on the first display unit and the narrow-band transmission characteristic displayed on the second display unit are observed and the measurement conditions are determined, easy observation and operation is ensured.
2. Description of the Related Art
Conventional techniques relating to the measurement and display of an input signal, as stated above, are disclosed in Published Unexamined Japanese Patent Application No. 59-95472 (hereinafter referred to as Prior Art 1) in which such techniques are applied to an oscilloscope.
In a waveform display, which was known before the filing date of Prior Art 1, it was necessary to make variable the gain of a vertical-axis amplifier or a horizontal-axis amplifier for driving a CRT (cathode-ray tube), in order to increase the amplitude or time axis of waveform. In this case, if the gain is varied at a variable DC level, the variable DC level is simultaneously increased. Consequently, if the the variable DC level is changed by the same degree as in the non-increase time, the display position of an enlarged display waveform moves to a greater degree than in the non-increase time. Since the display movement speed of the enlarged display waveform increases, it is difficult to suitably adjust the display position.
Under the situation, in the waveform display of Prior Art 1 wherein a waveform is displayed and a part of the displayed waveform is selected and enlarged, the ratio of enlargement is found when the displayed waveform is enlarged. In accordance with the ratio of enlargement, the movement speed of the waveform or cursor is decreased, and the adjustment of the display position is made easy.
In other words, in this art, the movement speed is decreased by the degree corresponding to the amplified variable DC level at the time of enlargement (i.e. corresponding to the above-mentioned ratio). For example, suppose that the knob on the panel for moving a cursor is operated (adjusted) by a predetermined degree, in order to move the cursor to a predetermined display point, while observing the display. Consequently, a signal (corresponding to the above-mentioned variable DC level) for moving the cursor is, in fact, output by a predetermined amount. At this time, the ratio (movement speed) between the degree of this operation (adjustment) and the actual movement distance of the cursor on the display is kept at a predetermined value, irrespective of the non-enlargement time or enlargement time. Thus, the operation of moving the waveform or cursor on the display is made easier.
A conventional spectrum analyzer is disclosed in U.S. Pat. No. 4,264,958 (hereinafter referred to as Prior Art 2). This spectrum analyzer employs a technique of so-called zoom function. During the measurement display in a given spectrum range, the frequency of a point designated by a marker or a peak point of the spectrum is used as a center frequency, and the band width is narrowed. The narrowed band width is measured and enlarged for display.
When Prior Art 1 is applied to a spectrum analyzer, the following problems will occur.
The device of Prior Art 1 is designed for measurement of a waveform in a time region, with use of an oscilloscope. If the waveform is enlarged for display, the measurement resolution is increased. Thus, the function itself of keeping the movement speed on the display at a constant value is effective.
However, a spectrum analyzer has not only the same display function as an oscilloscope, but also has a measuring unit for detecting the level of a spectrum in a frequency region. Thus, in the spectrum analyzer, when the band width for measurement is changed for enlarged measurement display, the display resolution based on frequency (frequency width per unit distance on the abscissa) is increased, even if the movement speed on the CRT display is unchanged like the oscilloscope. Under the situation, regarding the spectrum analyzer, since the measurement resolution of the measuring unit must be increased in accordance with the enlarged width, it is necessary to set the measurement resolution and sweep time of the measuring unit in accordance with the band width for enlarged measurement display and under optimal error-free conditions.
It should be noted that in the spectrum analyzer the measurement resolution and the sweep time of the measuring unit have the relationship: when the frequency is swept at a higher speed than the speed required when the measuring unit detects the level at a predetermined frequency resolution (hereinafter called "resolution"), the error increases, while the frequency is swept at a lower speed, the measurement precision is better but longer time is consumed.
Regarding the zoom function in Prior Art 2, where the enlarged display is restored to the normal (non-enlarged) display for measurement, the measurement conditions for the non-enlarged display must be set once again.
Neither Prior Art 1 nor 2 teaches the technical concept of the present invention: a wide-band spectrum and a narrow-band spectrum are measured and displayed and observation and operation can be carried out with a measurement resolution of the band width of each spectrum and, simultaneously, the condition changed for measurement in one band is reflected on the condition for measurement in another band. Thus, the conventional devices are inconvenient when the spectrum analyzer is used to alternately measure and display the wide-band spectrum and narrow-band spectrum and set and control the conditions therefor. There is a strong demand that these problems be solved urgently in the spectrum analyzer and the network analyzer.